Endoprosthetic bone joint devices

ABSTRACT

A hip joint prosthesis is provided with a socket member for the acetabular cavity and a cap member for the femoral head, both members being formed with grooves for fixation to exposed cancellous bone in association with gap-filling medium. The cap member has a major-spherical-segment outer bearing surface, and a coaxial cylindrical inner fixation surface with axial and circumferential grooves to receive said medium. The socket member has a spherically shaped inner bearing surface of not more than hemispherical extent to articulate with the cap member, and an outer fixation surface of hemispherical shape with coaxial annular grooves to receive said medium. The socket and cap members can be respectively of metal and plastics material, in which case the socket is of relatively thin, regular hemispherical form; or these materials can be reversed in which case the socket bearing surface is of minor-spherical-segment shape and can be eccentric to its fixation surface to provide greater thickness remote from its mouth.

United States Patent [191 Freeman et a1.

1 1 ENDOPROSTHETIC BONE JOINT DEVICES [75] Inventors: Michael AlexanderReykers Freeman, London; Sydney Alan Vasey Swanson, Carshalton, both ofEngland [73] Assignee: National Research Development Corporation,London, England 22 Filed: May 9,1974

21 Appl. No.: 468,583

[52] US. Cl. 3/l.9l2; 128/92 C, 128/92 CA [51] Int. Cl. .l ..A61F l/24[58] Field of Search 3/1, 1.9-1.913; 128/92 C, 92 CA, 92 R [56]References Cited UNITED STATES PATENTS 2,668,531 2/1954 Haboush 128/92CA 3,648,294 3/1972 Shahrestani 3/1 3,658,056 4/1972 Huggler et a1.....128/92 CA 3,685,058 8/1972 Tronzo 3/1 3,723,995 4/1973 Baumann 3/1FOREIGN PATENTS OR APPLICATlONS 2,096,895 3/1972 France 128/92 C1,047,640 7/1953 France 720,092 12/1954 United Kingdom 128/92 CA OTHERPUBLICATIONS Muller Total Hip Prosthesis (Advertisement page Dec. 16,1975 XXV), The Journal of Bone & Joint Surgery, British Vol. 53-B, No.3, Aug. 1971.

Primary Examiner-Ronald L. Frinks Attorney, Agent, or Firm-Cushman,Darby and Cushman [57] ABSTRACT A hip joint prosthesis is provided witha socket member for the acetabular cavity and a cap member for thefemoral head, both members being formedwith grooves for fixation toexposed cancellous bone in association with gap-filling medium. The capmember has a major-spherical-segment outer bearing surface, and acoaxial cylindrical inner fixation surface with axial andcircumferential grooves to receive said medium. Tne socket member has aspherically shaped inner bearing surface of not more than hemispherical5'Glaims, 8 Drawing Figures US. Patent Dec. 16, 1975 Sheet1of2 3,925,824

US. Patent Dec. 16,1975 Sheet2of2 3,925,824

ENDOPROSTHETIC BONE JOINT DEVICES This inventionconcerns endoprostheticbone joint devices and relates particularly, but not exclusively, tosuch devices for the hip joint.

In a more general aspect, the present invention provides anendoprosthetic bone joint device comprising: a pair of male and femalebearing components; the male component being in the form of acap memberhaving a convex bearing surface shaped as a surface of revolution abouta fixed axis, and a generally concave fixation surface behind saidconvexbearing surface; the female component being in the form of asocket member having a concave bearing surface substantiallycomplementary with said convex bearing surface for mutual articulatoryengagement therewith, and a generally convex fixationsurface behind saidconcave bearing surface; and said fixation surfaces having relievedformations of shallow depth relative to the transverse dimensions acrosssuch surfaces, which surfaces re-' ceive acrylic cement or equivalentgap-filling medium employed in securement of the components relative tobones of the relevant joint.

In a more particular aspect of the invention such a device is providedfor a hip joint prosthesis with said male and female components servingrespectively as femoral and acetabular components in the form of cap andsocket members having outer and inner substantially part-sphericalbearing surfaces.

Normally the two components of the proposed device will be maderespectively of metal and plastics material, and in the case of a hipjoint device it is presently preferred that the femoral and acetabularcomponents be respectively of metal and plastics material.

The above more general features of the invention are consideredadvantageous for several reasons. Firstly, both of the components of thedevice can be suffi-, ciently small to permit insertion substantially orentirely within the capsule of the relevant natural joint, therebypreserving to the greatest possible extent the ligamentous stability ofthe joint, and minimising the interface between .the device and thebones of the joint to reduce the riskof a post-operative infection andthe seriousness of theconsequences of any such infection which mayoccur. Secondly, the size, shape and mode of fixation of the componentsare such that implantationis simpler than conventionally the case,removal is simpler in the event of post-operative infection or othercauses, and greater scope is available compared to conventionalendoprosthetic situations for the adoption of alternative remedialmeasures in the event that the endoprosthesis is not completelysatisfactory. Thirdly, the bearing surfaces of the components can beshaped so as to constrain one component relative to the other incombination with theremaining ligamentous and muscular constraints, onlyso far as is necessary for functional stability of the joint, therebyreducing the likelihood of undesirable forces being transmitted throughthe device and tending to loosen the fixation of the components relative.to the bones of the joint. Fourthly, the preferred use of metal andplastics material can provide a low friction bearing relationshipbetween the two components with use of materials which are biologicallyinnocuous in respect of wear particles and other properties, and alsoprovide further advantages of relevance to specific joints.

For a=fuller and clearer understanding of the invention, two embodimentsof a hip joint device according thereto will now be described by way ofexample with reference to the accompanying drawings, in which! FIGS. 1and 2 respectively illustrate the acetabular component of a firstembodiment in plan and cross-sectional view, I

FIGS. 3 and 4 similarlyillustrate the associated femoral component ofthe first embodiment,

FIGS. 5 and 6 respectively illustrate the acetabular component of thesecond embodiment in plan and cross-sectional view, and

FIGS. 7 and 8 similarly illustrate the femoral component of the secondembodiment. a The acetabular component of FIGS. 1 and 2 comprises asocket member 1 having concentric hemispherical inner and outer surfaces2 and 3 which are coaxial 'in respect of their respective radial axes ofsymmetry.

The inner surface 2 serves as a bearing surface for and is provided witha smoothly rounded relieved area 4 around its rim to facilitate receiptof the latter component and to reduce the stresses otherwise associatedwitha square edge at this rim. The outer surface 3 is providedwithrelieved formations to afford an enhanced key for acrylic cement orequivalent medium used in securing the cup in as'uitably reamedacetabulum. These formations comprise three circular grooves 5 and threecircular areas 6, the grooves being'successively mutually spaced andconcentrically located. relative to the radial axis of symmetry of thesocket member, and the areas 6 being located in uniformcircumferentially spaced manner between the two grooves of smallerdiameter to bridge the same.

The associated femoral component of FIGS. 3 and 4 comprises a cap member7 having an outer surface 8 of major spherical seqment shaping which isof substantially identical radius as the inner surface 2 of the socketmember 1 in which it is received in bearing relation. The inner surface9 of the cap member 7 is of substantially right circular cylindricalshape coaxial with the longitudinal axis of symmetry of the outersurface 8. The inner surface 9 is provided with grooves 10 and 11 havinga similar function in relation to fixation of the cap member around asuitably reduced femoral head as the grooves of the socket member to theacetabulum. There are six uniformly circumferentially spaced grooves 10extending axially along the surface 9, and a single groove 11 extendingcircumferentially around the surface 9 at a position partway axiallytherealong. Regarding materials: the socket member 1 is presently madeof stainless steel and the cap member 7 of ultra high molecular weightpolyethylene. 1

The acetabular component of FIGS. 5 and 6 comprises a socket member 20having part-spherically shaped inner and outer surfaces 21 and 22. whichsurfaces are both symmetrical about a common radial axis. However unlikethe corresponding surfaces in the first embodiment, those at hand arenot concentric. The outer surface 22 is hemispherical, the innersurfaceis less than hemispherical, more specifically, minor spherical segmentshape, and the respective spherical cen-.

-As before, the inner surface 21 serves, as a bearing surface forengagement with the associated femoral component and is provided with asmoothly rounded relieved area 23, around its rim.

Also, as before, the outer surface is provided with relieved formationsfor the purposes of securement in association with cement in theacetabulum. In this instance these formations comprise two circulargrooves 24 which are mutually spaced, one adjacent the rim and the otherpartway towards the axis of symmetry, in concentric manner relative tosuch axis, and a circular area 25 concentrically embracing such axis. Inaddition, there are four quadrant form grooves 26 extending from thearea 25 at successive 90 spacings therearound to communicate with thegrooves 24 in mutually orthogonal manner.

The associated femoral component of FIGS. 7 and 8 comprises a cap member27 with outer surface 28, inner surface 29, axial inner grooves 30, andcircumferential inner groove 31 which are closely similar to thecorresponding features of the first embodiment femoral component. Twoexceptions to this similarity are that the inner surface 29 is morerounded in its innermost portion as seen in FIG. 8, and the axialgrooves 30 terminate in the circumferential groove 31.

Remaining differences between the first and second embodiment are thatin the latter the choice of component materials is reversed and thedifference in component wall thicknesses is less marked.

It is now appropriate to consider the common advantages of the twoillustrated embodiments and also their relative advantages.

A major advantage common to both embodiments is the use of a femoralcomponent in the form of a cap member which contrasts markedly with theconventional form of femoral head replacement device. The latter form ofdevice comprises an integral structure of a long intramedullary 'stemterminating, through a necked portion, in a ball-shaped head. Such adevice requires removal of the natural femoral head by sectioning of thefemoral neck, and receipt of the device stem in the medullary canalwhich is usually reamed for this purpose. Clearly the cap member of eachillustrated device embodiment, when compared to the conventional device,requires significantly less removal of bone, involves significantly lesspenetration of foreign matter into the bone for purposes of fixation, itis simpler to implant and remove, and its use is compatible withsubsequent adoption of a greater number of alternative remedialmeasures.

It is also appropriate to consider the relative advantages of the twodifferent forms of illustrated enbodiment. From a theoretical standpointthe first embodiment is more advantageous with its respective allocationof metal and plastics material to the acetabular socket member andfemoral head cap member. With this allocation the cap member can have amarkedly greater wall thickness than the socket member, with the capmember having a large external diameter in the context of femoral headreplacement. This large external diameter, in combination with thecorrespondingly large internal diameter of the socket member, provides alarge area over which the bearing load is spread and can be expected toreduce the rate of radially directed wear in the components, and it alsoreduces the likelihood of dislocation between the components. At thesame time, the greater wall thickness of the cap member appearsappropriate to the greater susceptibility to wear of plastics materialcompared to metal, while the otherwise adverse result of the largeinternal diameter 4 for the socket member can be compensated by the useof metal to allow the provision of a relatively thinwalled member whichdoes not necessitate extensive reaming of the acetabulum with theassociated risk of penetration.

Accordingly, the first embodiment appears to represent a consistent andadvantageous arrangement, but is subject to two inter-relatedprovisions. These provisions are that, notwithstanding the larger wallthickness of the femoral cap member, it should stillv be possible toprovide a sufficiently large internal surface area in this member forthe purposes of secure fixation over a femoral head reduced to provide agenerally complementary stem of cancellous bone, and this stem of boneshould not be liable to degeneration. In this connection, an additionaladvantage of the first embodiment arises in that the plastics materialof the cap member is radiotransparent and allows x-ray examination ofthe bone therewithin to monitor the bone condition. In fact developmentand clinical testing of this first embodiment over a period of two yearsindicates that the relevant two provisions can be met.

I-Iowever, continued laboratory testing of this first embodimentindicates that, while from a theoretical standpoint an advantageouslyreduced rate of wear can be expected, the rate of wear will be greaterthan that with the second embodiment. Study of this unexpectedphenomenon continues but no fully substantiated explanation has yet beenestablished. In these circumstances, having established that use of theproposed femoral head cap member is practicable, it is consideredappropriate to pursue use of the second embodiment for reason of itslesser rate of wear, but subject to two provisions which are, again,inter-related.

These provisions are that the use of a thicker-walled socket member ofplastics material, in association with a metal femoral cap member ofsimilar dimensionsto those already established as satisfactory with thefirst embodiment, should not require unduly excessive reaming of theacetabulum and/or reduce the range of free articulatory movement withthe cap member by virtue of impaction between the natural femoral neckand the socket memberqIn practice these provisions can be met on thebasis of the finding during development and testing of the firstembodiment that the natural acetabular cavity is normally sufficientlydeep and extensive to accommodate a size' of socket member larger thanthose now in general use, and the fact that the inner surface of thesocket member can be less than fully hemispherical and still afford anadequate range of articulation for the cap member without undue risk ofdislocation. Accordingly, in'the second embodiment, the inner surface ofthe socket member is less than hemispherical, the outer surface remainshemispherical to facilitate securement in a conventional mammner, andthese two surfaces are mutually eccentrically located to provide notonly a thicker wall therebetween but a varying thickness which is at amaximum in the region of likely wear, the otherwise adverse effect onthe articulation range of the thicker wall at the rim of the socketmember being compensated by the reduced angular extent of the innersurface.

While this last discussion centres on the present preference for use ofthe second embodiment, others may take the view that the greater rate ofwear found with the first embodiment is not such as to outweigh itsother advantages. Alternatively, an understanding of the reasons forthis greater wear rate may allow the with its inner and outer surfacesboth being sub-.

stantially hemispherical and concentrically located to define a thinuniform thickness therebetween,

and a femoral component in the form of a cap member having an outerbearing surface of convex majorspherical-segment shape in complementary,mutually articulatory engagement with said inner bearing surface, and aconcave inner fixation surface of generally cylindrical shape coaxialwith the axis of symmetry of said outer bearing surface and formed witha shallow relieved configuration,

said cap member being fomied of a plastic material of significantlygreater thickness between its respective inner and outer surfaces thansaid acetabular component;

both of said fixation surfaces having relieved formations for receivinggap-filling medium in respective direct securement with the acetabulumand femur.

2. An endoprosthetic hip joint device comprising:

an acetabular component in the form of a socket member having an innerbearing surface concavely spherically shaped to not more thanhemispherical extent, and a hemispherically shaped outer fixationsurface formed with a shallow relieved configuration,

said inner bearing surface being of a minor spherical segment shapecoaxial with said outer fixation surface, but having its sphericalcenter displaced from that of said outer fixation surface to providesaid socket member with the greatest thickness remote from its mouth,said socket member being formed of an integral plastic material;

and a femoral component in the form of a cap member having an outerbearing surface of convex majorspherical-segment shape in complementarymutually articulatory engagement with said inner bearing surface, and aconcave inner fixation surface of generally cylindrical shape coaxialwith the axis of symmetry of said outer bearing surface and formed witha shallow relieved configuration, said 6 cap member being formed of ametal material; both of said fixation surfaces having relievedformations to receive gap-filling medium in respective direct securementwith the acetabulum and femur.

3. A device according to claim 2 wherein said displacement of sphericalcentres is in the associated coaxial direction.

4. An endoprosthetic hip joint device comprising:

an acetabular component in the form of a socket member of integral metalconstruction having an inner bearing surface and outer fixation surface,which surfaces are of concentric substantially hemispherical shapedefining a thin thickness theretween, and said outer fixation surfacehaving a shallow relieved formation to receive gap-filling medium insecurement with the acetabulum;

and a femoral component in the form of a cap mem- 5. An endoprosthetichip joint device comprising: an acetabular component in the form of asocket member of integral plastic construction having an inner bearingsurface of minor-spherical-segment shape and an outer fixation surfaceof hemispherical shape, said inner bearing and outer fixation surfaceshaving coaxial axes of symmetry, but eccentrically disposed respectivespherical centres to provide greater thickness between such surfacesremote from their peripheral edges, and said outer fixation surfacehaving a shallow relieved formation to receive gap-filling medium insecurement with the acetabulum;

and a femoral component in the form of a cap member of integral metalconstruction having an outer bearing surface of major-spherical-segmentshape in mutual articulatory engagement with said inner bearing surface,and an inner fixation surface of generally cylindrical shape, said innerfixation surface having grooves in the axial and circumferentialdirections of its cylindrical shape to receive gap-filling medium indirect securement with the femur.

1. An endoprosthetic hip joint device comprising: an acetabularcomponent in the form of a socket member having an inner bearing surfaceconcavely spherically shaped to not more than hemispherical extent, anda hemispherically shaped outer fixation surface formed with a shallowrelieved configuration, said socket member being formed of metal withits inner and outer surfaces both being substantially hemispherical andconcentrically located to define a thin uniform thickness therebetween,and a femoral component in the form of a cap member having an outerbearing surface of convex majorspherical-segment shape in complementary,mutually articulatory engagement with said inner bearing surface, and aconcave inner fixation surface of generally cylindrical shape coaxialwith the axis of symmetry of said outer bearing surface and formed witha shallow relieved configuration, said cap member being formed of aplastic material of significantly greater thickness between itsrespective inner and outer surfaces than said acetabular component; bothof said fixation surfaces having relieved formations for receivinggap-filling medium in respective direct securement with the acetabulumand femur.
 2. An endoprosthetic hip joint device comprising: anacetabular component in the form of a socket member having an innerbearing surface concavely spherically shaped to not more thanhemispherical extent, and a hemispherically shaped outer fixationsurface formed with a shallow relieved configuration, said inner bearingsurface being of a minor spherical segment shape coaxial with said outerfixation surface, but having its spherical center displaced from that ofsaid outer fixation surface to provide said socket member with thegreatest thickness remote from its mouth, said socket member beingformed of an integral plastic material; and a femoral component in theform of a cap member having an outer bearing surface of convexmajorspherical-segment shape in complementary mutually articulatoryengagement with said inner bearing surface, and a concave inner fixationsurface of generally cylindrical shape coaxial with the axis of symmetryof said outer bearing surface and formed with a shallow relievedconfiguration, said cap member being formed of a metal material; both ofsaid fixation surfaces having relieved formations to receive gap-fillingmedium in respective direct securement with the acetabulum and femur. 3.A device according to claim 2 wherein said displacement of sphericalcentres is in the associated coaxial direction.
 4. An endoprosthetic hipjoint device comprising: an acetabular component in the form of a socketmember of integral metal construction having an inner bearing surfaceand outer fixation surface, which surfaces are of concentricsubstantially hemispherical shape defining a thin thickness theretween,and said outer fixation surface having a shallow relieved formation toreceive gap-filling medium in securement with the acetabulum; and afemoral component in the form of a cap member of integral plasticsmaterial construction having an outer bearing surface ofmajor-spherical-segment shape in mutual articulatory engagement withsaid inner bearing surface, and an inner fixation surface ofsubstantially cylindrical shape coaxial with the axis of symmetry ofsaid outer bearing surface, said outer bearing and inner fixationsurfaces defining a significantly greater thickness therebetween forsaid cap member than said socket member, and said inner fixation surfacehaving grooves in the axial and circumferential directions of itscylindrical shape to receive gap-filling medium in direct securementwith the femur.
 5. An endoprosthetic hip joint device comprising: anacetabular component in the form of a socket member of integral plasticconstruction having an inner bearing surface of minor-spherical-segmentshape and an outer fixation surface of hEmispherical shape, said innerbearing and outer fixation surfaces having coaxial axes of symmetry, buteccentrically disposed respective spherical centres to provide greaterthickness between such surfaces remote from their peripheral edges, andsaid outer fixation surface having a shallow relieved formation toreceive gap-filling medium in securement with the acetabulum; and afemoral component in the form of a cap member of integral metalconstruction having an outer bearing surface of major-spherical-segmentshape in mutual articulatory engagement with said inner bearing surface,and an inner fixation surface of generally cylindrical shape, said innerfixation surface having grooves in the axial and circumferentialdirections of its cylindrical shape to receive gap-filling medium indirect securement with the femur.